With the development of wireless communications technologies, wireless communications base stations are more densely distributed, imposing increasingly strong requirements for miniature base stations. A radio frequency front-end filter module in a base station occupies a relatively large volume; therefore, using a filter with a smaller volume plays an important role in reducing the volume of the base station.
There are many types and forms of filters, among which, a dielectric filter has a relatively small volume. FIG. 1 shows an existing dielectric filter. A body of the dielectric filter is a dielectric 11 in a rectangular shape, where a through hole 12 is disposed in the dielectric 11, one end of the through hole 12 is exposed from the front face of the dielectric 11, and the front face of the dielectric 11 is partially metalized, that is, a square metal layer 13 is formed only on a dielectric 11 surface surrounding the end of the through hole 12, adjacent square metal layers 13 are electrically insulated, and except the front face, all other surfaces of the dielectric 11 are metalized (in FIG. 1, shadowed parts are metalized areas, and unshadowed parts are non-metalized areas). One through hole 12 and the square metal layer 13 surrounding the end of the through hole 12 on the front face of the dielectric 11 form one dielectric resonator, where a resonance frequency of the dielectric resonator is adjusted by adjusting an area of the square metal layer 13, and coupling between adjacent dielectric resonators is adjusted by adjusting a distance between the adjacent square metal layers 13.
In the foregoing dielectric filter, an inner resonance mode of the dielectric resonator is a TEM (Transverse Electromagnetic) mode, and loss of an inner conductor is large, which leads to large loss of the dielectric filter. As a result, a loss indicator of the dielectric filter cannot meet a filtering requirement of a base station.